This invention relates to acoustical structures generally and, more particularly, to a strong, lightweight composite panel capable of absorbing sound so as to reduce sound reflected from or transmitted through the panel.
Various space dividers of prefabricated composite panels are commonly used in commercial buildings for dividing an interior space into work areas. Such space dividers may include a frame for reinforcing the panels and a stand or legs for supporting the panels in a vertical plane. These space dividers have proven effective in providing privacy within a building while improving the interior appearance of the work space. The composite panels used in such space dividers may be provided with soft exterior finishes to absorb sound, for example, by covering with carpeting or fabric, or may be provided with a decorative covering material to improve their appearance.
Similar prefabricated composite panels are commonly used as ceiling tiles, wall panels, bulletin boards, partitions or enclosures, and other building elements. Each of these applications has particular requirements favoring a somewhat different acoustical structure. For example, structural rigidity, strength, fire resistance, thermal insulating ability, impact resistance, and smoothness or tackability of the surface may be required in addition to the ability to reduce transmitted or reflected sound. Mounting requirements may create particular problems.
Various structures have been proposed to provide a prefabricated panel capable of absorbing a high percentage of incident sound, i.e., sound directed normal to the panel or at other angles of incidence. One approach has been to provide a homogeneous fiberglass core reinforced by a rectangular perimeter frame and having a fabric covering. However, such panels do not possess sufficient strength and rigidity for many applications. Other panel designs have utilized a laminated honeycomb structure to reinforce a sound deadening material to provide a lightweight semi-rigid panel, such as that proposed in U.S. Pat. No. 3,021,916.
Such panels having a honeycomb core are normally laminated or faced by a hot press or cold press method. In each case, an adhesive is applied to the facing and/or to the honeycomb core before the laminations of the panels are stacked and exposed to pressure while the adhesive cures. A hot press is used if the adhesive must be cured at high temperatures. In some cases, the core is crimped to provide a glue shelf for the application of the adhesive. However, the adhesives of such panels inhibit the sound absorbing qualities of the panels and do not provide adequate resistance to delamination in shear when the panels are subjected to bending.
Another proposed panel construction is an assembly of separate layers of homogeneous fiberglass of different densities. For example, such a panel might have a fabric covering, a 1/8 inch layer of compressed fiberglass board, a 3/4 inch layer of low density fiberglass, a 20 gauge metal pan, a second 3/4 inch layer of low density fiberglass, a second 1/8 inch layer of compressed fiberglass board, and a second fabric covering. This type of panel construction is expensive, particularly because the pan must be made of metal to provide the necessary strength and because the finished panel must be assembled of separate layers instead of by insertion of a prefabricated panel board.
It has also been proposed that a honeycomb core be used on opposite sides of a septum or divider, as disclosed in U.S. Pat. No. 4,084,367. The panel structure proposed therein includes apertured sheetmetal skins providing a single, small opening to each cell of the honeycomb core to form Helmholtz resonators for trapping sound energy. However, the sheetmetal skins forming the exterior walls of the Helmholtz resonators reflect a large percentage of the incident sound back into the working area. Furthermore, each of the Helmholtz resonators can only be tuned to absorb a single sound frequency corresponding to the volume of the cell.
A need exists for an improved composite panel structure suitable for use in space dividers, ceiling tiles, wall panels, blackboards or bulletin boards, partitions or enclosures, and other building elements. In addition to enhanced acoustical properties, the structure should provide appropriate structural rigidity, strength, fire resistance, thermal insulating ability and surface texture for each application. The structure should provide improved resistance to delamination in shear and should be suitable for low cost manufacture as a prefabricated panel in various thicknesses and configurations.
It is therefore an object of the present invention to provide a low cost composite panel structure having strength and rigidity and providing improved absorption of sound energy over that which can be obtained with a comparable thickness of homogeneous absorption material. It is a further object of the present invention to provide such a structure having improved absorption capability on one or both sides of a panel in combination with an acoustical barrier to prevent the transmission of sound through the panel. It is a further object of the present invention to provide such a structure with an impact resistant or tackable surface and with various core configurations which may include a molded-in frame.